Global radio spectrum acquisition has resulted in the heavy use of several frequency bands for certain communication standards. Modern cellular communication often demands a multi-band approach to radio frequency (RF) transceivers. For example, a RF engine of a transceiver can be designed to switch, using “software-defined” switches, between different receive bands. Communication systems using a frequency-division duplexing (FDD) mode, or the like, can be more affected by the use of multi-band spreading, since their seamless duplex communication relies on a minimum isolation of receive (Rx) and transmit (Tx) paths.
One approach to providing front-end isolation between the Tx and Rx is based on using a duplexer. A duplexer includes two narrowband band-pass filters with a very-high quality factor. The duplexer attempts to provide the desired Tx to Rx isolation by passing receive and transmit bands through passband filters with a very sharp flank. The required high-Q filter can be achieved by special and often expensive process technologies, like surface or bulk acoustic waves (SAW/BAW) technologies, for example. However, the narrowband characteristic of the filter and its lack of tunablility allows the application of one duplexer for each band. So, the quantity of duplexers and associated input ports on a RF transceiver increases with the number of supported bands. The cost of supporting multiple bands is reflected in additional bill of materials (BOM) as well as increases in engine area and potentially the amount of RF I/O ports of chip.